Metallic glasses have properties such as high corrosion resistance, high strength, and high toughness. However, some metallic glass-forming alloys have limited glass-forming ability, which can present a challenge in forming bulk metallic glass objects or parts (e.g., objects or parts larger than 1 mm).
The largest thickness that a metallic glass can be formed from a given alloy composition is linked to the cooling rate required to bypass the formation of the stable crystalline phase. The lower this “critical” cooling rate is, the larger the “critical” thickness of the metallic glass. The empirical relationship linking the critical cooling rate Rc in K/s and the critical thickness tc in mm is given by:Rc=1000/tc2  Eq. (1)
Generally, three categories are known in the art for identifying the ability of a metal alloy to form a metallic glass (i.e. to bypass the stable crystal phase and form an amorphous phase). Metal alloys having critical cooling rates in excess of 1012 K/s are conventionally referred to as non-glass-formers, as they are physically unattainable to achieve such cooling rates for a bulk thickness. Metal alloys having critical cooling rates in the range of 105 to 1012 K/s are conventionally referred to as marginal glass-formers, as they are able to form glass over thicknesses ranging from 1 to 100 micrometers according to Eq. (1). Metal alloys having critical cooling rates on the order of 103 or less, and as low as 1 or 0.1 K/s, are conventionally referred to as bulk glass-formers, as they are able to form glass over thicknesses ranging from a millimeter to several centimeters.
Bulk metallic glass parts are often manufactured from alloy compositions that are considered bulk glass-formers. In various manufacturing processes, a feedstock sample formed of a bulk amorphous glass forming alloy can be heated and molded into a bulk object or part. However, alloy compositions that are conventionally considered bulk amorphous glass-formers are limited. Further, various manufacturing processes generally require that metallic glass-forming alloy feedstock be a monolithic sample.